Embodiments of the subject matter disclosed herein relate to a mechanism for enabling independent pitch control of airfoil blades of contra-rotating rotor assemblies. The application is of particular benefit when applied to “open rotor” gas turbine engines.
Gas turbine engines employing an “open rotor” design architecture are known. The open rotor design is essentially a hybrid of conventional turbofan and turboprop gas turbine engines, but providing enhanced fuel efficiency over both conventional engine designs. A turbofan engine operates on the principle that a central gas turbine core drives a bypass fan, the fan being located at a radial location between a nacelle of the engine and the engine core. An open rotor engine instead operates on the principle of having the bypass fan located outside of the engine nacelle. This permits the use of larger fan blades able to act upon a larger volume of air than for a turbofan engine, and thereby helps to generate more thrust than for conventional engine designs. Optimum performance has been found with an open rotor design having a fan provided by two contra-rotating rotor assemblies, each rotor assembly carrying an array of airfoil blades located outside the engine nacelle. In appearance, the fan blades of an open rotor engine resemble the propeller blades of a conventional turboprop engine.
The use of contra-rotating rotor assemblies provides technical challenges in transmitting power from the turbine core to drive the airfoil blades of the respective two rotor assemblies in opposing directions.
EP1881176A2 (Rolls-Royce plc, 23 Jan. 2008) discloses an engine conforming to an open rotor design architecture, the engine having a mechanism for enabling independent pitch control of respective airfoil blades of a first rotor assembly and a second rotor assembly, where the first and second rotor assemblies are driven in a contra-rotating manner about a longitudinal axis of the engine.
Embodiments of the present invention seek to provide an improved alternative to the engine arrangement disclosed in EP1881176A2, and to provide improvements in efficiency over known designs.